Things you don't hear from gunfight survivors
1. I wish I had less ammo.
2. I wish I used a less effective caliber/type of ammo.
3. I wish I practiced less.
4. I wish my gun was less accurate.
5. I wish I was less accurate.
6. I wish I had not found cover or found less cover.
7. I wish the police got there later to help me.
8. I wish my gun was less reliable.
Are 5 shots enough for the situation you described? Well, if you don't actually have to fire the gun, then you had plenty. Five shots for three attackers, however, very well may not be enough if you actually need to shoot all of them. There is a good likelihood that you will miss with most or many of your shots. Of those shots you land, there is a strong likelihood that they will not incapacitate each bad guy as chances are that you are not going to be able to land your shots in the correct place to accomplish the task.
The argument that semi-autos are less reliable and that you might lose precious time clearing a malfunction may be a valid point. That being said, semi-autos are quicker to reload as well as carry more ammo in the gun before the need arises. If you do have a malfunction in a semi-auto, quite likely it will be one that can be cleared fairly quickly and easily with the Tap-Rack procedure. In a revolver, reload will be slower, plus if you do have a malfunction, chances are that it will be terminal for the situation. In other words, it can be very difficult to fix a revolver malfunction as well as being very slow.
Something else to consider, most revolvers today are DAO with fairly heavy and long trigger pulls. Those two traits do not lend themselves to producing accurate shooting for ineperienced shooters. This is something Ayoob talked about in Gravest Extreme. In many police shootings where the gun carried was DA for the first round and SA for subseqent rounds, Ayoob found that the accuracy of the DA rounds tended to be very poor as compared to the later single action rounds. That being said, a well trained shooter will be able to shoot a revolver just as accurately inspite of the trigger and can actually shoot the gun faster than what many semi-autos are capable of doing. Few civilians take enough time to be that proficient with revolvers.
GrantLee63 is right that chances are that you will never need to shoot your gun at somebody. However, should you need to do so, then you are going to want to be able to deliver as many rounds as needed on target(s) and so if that should happen, five shots probably will not be enough. Following that logic, don't waste time or money on more expensive larger calibers. Just go ahead and get a SA NAA Mini revolver loaded with .22 shorts. Heck, don't even bother with carrying a gun as the odds are that you will never have to use it.
Something else to consider. Whether or not you feel outgunned with a particular weapon is not all that terribly relevant except for your own piece of mind. What is relevant is whether or not you are actually outgunned in a situation.
4V50 Gary is right that 5 shots to the brain generally removes that one threat, but the situation described has three bad guys. So you put five shots into the brain of one of them. Now you have two more to face and an empty gun.
Also, in the Miami FBI shootout, but bad guys were hit in the head. Matix was struck twice in the head by .38 Special 158 gr. lead hollowpoint ammo. One shot was to the side of the cranium at the temporal bone which had the brains right behind it. However, the round did not penetrate the brain case at all. The other shot did not penetrate beyond the cheek bone under the eye. Platt was shot on the side of the forehead by the same ammo and that round failed to penetrate and simply skid around outside of the brain case and under the skin.
The brain is a fairly small target to try to hit and this is made even more difficult when the shots are on target, but don't have the capability to penetrate the bone and enter the brain.